wrote in message
...
On Tue, 18 Mar 2014 00:09:04 -0700, "Bob La Londe"
wrote:

"Gunner Asch" wrote in message
. ..
On Sun, 16 Mar 2014 15:13:20 -0700, wrote:

On Sat, 15 Mar 2014 21:04:22 -0400, Ned Simmons
wrote:

On Sat, 15 Mar 2014 09:52:22 -0700, wrote:

I'm building an engraving spindle using a high speed bldc motor made
for a model airplane. Today I'll be testing the first iteration at
about 14,400 rpm. This is the highest speed my motors will go. If the
test goes OK I'll be buying higher speed motors and will need
bearings. My plan is to use ER8 collets in an ER8 holder that has a
10mm OD. So the ER8 holder will be the spindle. Which means the
bearings will have a 10mm ID and a max OD of 30mm in order to fit into
the spindle housing which will fit into a 1.5 ID tool holder. I think
what I want is a couple deep groove bearings. The axial and radial
loads will be small but the RPM so high that the dynamic load may be
high. I will try using the load calculator at the SKF website but
would also appreciate advice from folks here who do this kind of thing
and can steer me in the right direction. Even though the SKF website
has all sorts of great info I have been unable to find an SKF ball
bearing catalog online. I need this in order to plug the right SKF
part number into the bearing calculator.
Thanks,
Eric


First you ought to decide how stiff you'd like your spindle to be.
Simplest and cheapest will be a pair of deep groove bearings with a
spring preload. If you want stiffness more like a milling or grinding
spindle you'll need to go to a precision angular contact pair in order
to get the preload right.

Springs will make setting the preload relatively easy with regular
deep groove bearings, but with a sacrifice of stiffness. Springs =
springy.

And the preload is critical at these speeds.

This would be a suitable angular contact pair. Light preload, 15
degree contact angle.
http://www.ebay.com/itm/FAFNIR-MODEL...-/250320797407

If you use deep groove bearings, I'd suggest SKF's electric motor
quality bearings. They're claimed to be a couple grades higher than
their ABEC1 rating in a few areas, including runout. I think "JEM" in
the SKF number is what you're looking for.

You'll also need to decide whether to use a pair of bearings at the
spindle nose plus a single floating bearing at the tail, or two
bearings separated by spacers. Easy to do with spring preload,
requires substantial care otherwise.

Lubrication will also be critical. Kluber Isoflex NBU15 grease is
probably OK, but Kluber may be able to recommend something else. I've
found them helpful on the phone on a couple occasions.

Barden, NSK, and Fafnir seem to have better info that SKF on precision
and high speed bearings.

By the way, if you're using "dynamic load" as it's presented in the
bearing manuals, I think you're misinterpreting what it means. The
dynamic load rating is used to predict the time to failure of a
bearing by fatigue of the balls or races. The static load rating is
the load that will cause a permanent deformation of a specific
magnitude in the balls and races.
Greetings Ned,
The reason I'm looking at dynamic load is because of the lifetime. I
was surprised to see lifetimes of about 40 hours, and even less, for
some bearings. I would really like to only put in one set of bearings.
I'm not sure how stiff the thing needs to be. It will be used with
standard engraving tools and maybe with endmills up to about .187 max
diameter. But most likely just for engraving.
Thanks,
Eric.

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Consider that the lifetime means generally the time the spindle is
turning and most often under load. Then consider how much 40 hours of
run time really is on an engraver.


Maybe only as long as a few weeks on a busy machine. Somebody programming
engraving is going to want to keep the cutter engaged as much as possible
to
get he job done and get on to the next job.


Another potential off the shelf engraving tool is one of the higher end
Foredom rotary hand pieces. Still not 40K, but in that 15-18 K range. Not
the ones that sell for 50-75 ones. They are fitted to losse so they can
keep the price down and have modestly long life You want the one that sell
for around 150-175 if you want to try that. Contact Foredom first to get
the model number of the heavy duty one. You might be able tot fit that one
in your tool holder if you can figure out how to drive it.






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